<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        div {
            width: 400px;
            height: 400px;
            border: 1px solid black;

            margin: 0 auto;

            /* border-radius: 200px; */
            border-radius: 10%;
        }
    </style>
</head>
<body>

    <div></div>
    
</body>
</html>